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Mon. Not. R. Astron. Soc. 000, 1{15 (0000) Printed 1 November 1999 (MN L A T E X style le v1.4) The evolution of a rapidly accreting helium white dwarf to
 

Summary: Mon. Not. R. Astron. Soc. 000, 1{15 (0000) Printed 1 November 1999 (MN L A T E X style le v1.4)
The evolution of a rapidly accreting helium white dwarf to
become a low-luminosity helium star
Hideyuki Saio 1 and C. Simon Je ery 2
1 Astronomical Institute, School of Science, Tohoku University, Sendai 980, Japan
2 Armagh Observatory, College Hill, Armagh BT61 9DG, Northern Ireland
Accepted . Received ;
ABSTRACT
We have examined the evolution of merged low-mass double white dwarfs which be-
come low-luminosity (or high-gravity) extreme helium stars. We have approximated
the merging process by the rapid accretion of matter, consisting mostly of helium, onto
a helium white dwarf. After a certain mass is accumulated, a helium shell ash occurs,
the radius and luminosity increase and the star becomes a yellow giant. Mass accre-
tion is stopped arti cially when the total mass reaches a pre-determined value. As the
helium burning shell moves inwards with repeating shell ashes, the e ective temper-
ature gradually increases as the star evolves towards the helium main sequence. When
M r
( ame) ' 0:25 M , the star enters a regime where it is pulsationally unstable. We
have obtained radial pulsation periods for these models.
These models have properties very similar to the pulsating helium star V652 Her.

  

Source: Armagh Observatory

 

Collections: Physics